Thermal spraying, and particularly plasma spraying and high velocity oxygen fuel (HVOF) spraying, are well established processes used in many metallurgical manufacturing processes. Thermal spraying is done normally in a thermal spray booth or enclosure.
The primary role of a thermal spray enclosure is to contain and/or control various hazards associated with thermal spray processing of materials. Historically, thermal spray booths were used to shield the shop floor from the intense sound pressures, dust and fumes, and ultraviolet light generated during spray operations. In the past years, the introduction of robotics has led to an expanded role for booths as barriers to protect humans from being struck by fast-moving robotic arms. The most modern spray enclosures are now designed to minimize operator exposure to a variety of thermal spray hazards. Spray boxes and fully automated spray booths that do not require an operator to be present in the spray environment are becoming more common, and in many situations have become an accepted requirement.
The use of an enclosed space to reduce hazards has considerably increased the safety of thermal spray operators and shop personnel that work in the vicinity of thermal spray devices. However, an enclosure introduces new hazards that must be addressed. A wide variety of gases are used in thermal spray processing. Unless proper care is taken, it is possible to create dangerous situations within an enclosure. An inert gas leak can displace the air, leading to an asphyxiation hazard. A fuel leak or build-up of an explosive metal powder can set up the possibility of a violent explosion. Thermal spray enclosures must be designed to provide simple egress of operators during an emergency situation. Operators inside a spray booth may be unaware of emergency situations on the shop floor, such as fire alarms, unless special provisions are made.
The thermal spray enclosure is the most important safety device used in thermal spray processing. Because the spray operations are conducted within its confines, all of the energy sources (gas, electricity, and water), the feedstock materials, and all of the process effluents (heat, dust, fumes, sound and ultraviolet light) are present. Proper mitigation of all of these hazards requires careful thought in the design and operation of a spray booth.
One concern that is important is to protect operators from point source radiation generated by thermal spray processes, particularly plasma and high velocity oxy-fuel (HVOF) spray processes. Operators need to view the process so they do not crash the robotic arm holding the spray device. Window tinting for plasma spray is too dark when the chamber is used for HVOF spraying. Conversely, the HVOF tint can cause eye fatigue and irritation when the chamber is used for plasma spraying.
The use of the same thermal spray chamber for plasma spray and HVOF spray processes allows for improved efficiency of a spray facility. Accordingly, allowing the operator to view the spray process without eye fatigue or eye damage is important.